Recently, such various devices and technologies requiring high data traffic as M2M (machine-to-machine) communication, a smartphone, a tablet PC and the like are emerged and disseminated. As a result, data traffic required to be processed in a cellular network is rapidly increasing. In order to satisfy the rapidly increasing data processing demand, a carrier aggregation technology, a cognitive radio technology, and the like are developing to efficiently use more frequency bands. And, a multi-antenna technology, a multi-base station cooperation technology, and the like are developing to increase data capacity transmitted in a limited frequency band. Communication environment is evolving to a direction that dense of neighboring nodes capable of being accessed by a user equipment is increasing. In this case, a node corresponds to a fixed point capable of transmitting and receiving a radio signal with a user equipment by installing one or more antennas in the node. A communication system equipped with nodes of high density can provide a communication service of higher performance to a user equipment with the help of cooperation between nodes.
According to a multi-node cooperative communication scheme performing communication with a user equipment using an identical time-frequency resource in a plurality of nodes, the multi-node cooperative communication scheme has vastly superior performance compared to a legacy communication scheme performing communication with a user equipment in a manner that each of a plurality of the nodes operates as an independent base station without any cooperation.
In a multi-node system, cooperative communication is performed using a plurality of nodes of which each node operates as a base station, an access point, an antenna, an antenna group, a radio remote header (RRH) or a radio remote unit (RRU). Unlike a legacy centralized antenna system of which antennas are concentrated on a base station, a plurality of the nodes are generally positioned in a manner of being apart from each other more than a prescribed space in the multi-node system. A plurality of the nodes can be managed by one or more base stations or a base station controller configured to control operation of each node or schedule data to be transmitted or received via each node. Each node is connected with a base station managing the node or the base station controller via a cable or a dedicated line.
The multi-node system may correspond to a sort of MIMO (multiple input multiple output) system in a point that distributed nodes are able to communicate with a single or a plurality of user equipments in a manner of transmitting/receiving streams different from each other at the same time. Yet, since the multi-node system transmits a signal using nodes distributed in various positions, a transmission region covered by each antenna is reduced compared to antennas installed in a legacy centralized antenna system. Hence, compared to the legacy centralized system in which MIMO technique used to be implemented, in the multi-node system, transmission necessary for each antenna to transmit a signal can be reduced. And, since a transmission distance between an antenna and a user equipment is reduced in the multi-node system, a path loss is reduced and fast transmission of data can be enabled. By doing so, transmission capacity and power efficiency of a cellular system can be enhanced and communication performance of relatively uniform quality can be satisfied irrespective of a position of a user equipment in a cell. And, since a base station(s) connected with a plurality of nodes or a base station controller(s) is cooperative in data transmission/reception, a signal loss occurring in a transmission process can be reduced. And, if nodes apart from each other more than a prescribed distance perform cooperative communication with a user equipment, correlation between antennas and interference can be reduced. Hence, according to the multi-node cooperative communication scheme, higher SINR (signal to interference-plus-noise ratio) can be obtained.
Hence, the multi-node system is coming to the fore as a new basis of a cellular communication instead of or together with a legacy centralized antenna system not only to expand service coverage and enhance channel capacity and SINR but also to reduce cost for installing more base stations and cost for maintaining a backhaul network in a next generation mobile communication system with the help of the strong point of the multi-node system.
Yet, if cooperative scheduling between multiple nodes is not achieved in the multi-node system, the strong points of the multi-node system are to be diluted due to interference between the multiple nodes. In particular, the aforementioned problems can be worsened in a wireless communication system in which such small scale cells as pico cells or femto cells are distributed. Hence, it is necessary to have a method of controlling the inter-cell interference in environment of the small scale cells.